It has been found that piston-type internal combustion engines, which are designed in accordance with unit construction principles and are directly or indirectly air-cooled, require cooling air flow proportional to the number of cylinders and, as the case may be, to the cooling performance of additional heat exchangers or coolers, while the necessary cooling air pressure is only slightly dependent upon the number of cylinders and the additional coolers. Since it is not economical to develop and fabricate a distinct blower for each engine in a series or family of engines having a different number of cylinders and different auxiliary cooler arrangements, one is forced to find compromise designs for blowers which aim toward the lowest possible number of blower sizes for a given range of variation in the number of cylinders and the performance requirements of additional coolers in the engine series.
There exist known axial blowers which are designed in accordance with the unit construction principles to meet the varying requirements for volume delivery, delivery pressure, speed and outside diameter. In such blowers the outside diameter, hub diameter and blade height are varied independently, or in reasonable combinations, with the variation from blower to blower always changing both the impeller and guide wheel. Because of this, these blowers have, in spite of the principle of unit construction, the disadvantage of a considerable number of distinct design components which is especially disadvantageous when the blower components are pressure-die cast.